Richard Alderman, head of the Serious Fraud Office, plans to press ahead with a controversial £30m plea bargain with the arms company BAE, legal sources say, despite criticism of such deals from a senior judge and anti-corruption campaigners.

Two protesting groups took his BAE deal to court, saying it was too soft, but a judge ruled against them. The Cornerhouse and the Campaign Against Arms Trade will decide whether to pursue an appeal after Easter. If their legal challenge is dropped, the way will then be clear for the deal thrashed out with BAE's lawyers to go ahead.

But the arms giant may end up facing the prospect of a bigger fine. Lord Justice Thomas gave a landmark ruling earlier this month in another corruption case, involving the chemical firm Innospec, that the agreed fine was too low, and such corporate crime should be treated more seriously.

Legal sources said today that the Thomas ruling should significantly increase the "fear factor" among companies alleged to have been paying bribes to make foreign sales. But it may also make future deals harder, by increasing the level of uncertainty about penalties.

Alderman is expected to hold talks with the judges in an effort to agree the best way to structure future plea bargains. The government's long-awaited bribery bill is also expected to pass into law, making future corporate convictions more likely.

In the present controversial plea deal, BAE has agreed to admit relatively minor accounting offences in respect of an overpriced military radar sold to Tanzania.

The company has already made a much bigger global settlement with the department of justice in Washington, paying $400m to settle accusations over jet fighter sales to Saudi Arabia and the Czech Republic.

Dick Olver, BAE's chairman, says in this week's annual report: "The company very much regrets and accepts full responsibility for these past shortcomings."

BAE has also finally taken Sir Dick Evans, its former chairman, off its payroll. Evans formally stepped down as BAE first came under investigation in 2004, but carried on as a £250,000-a-year consultant. His contract ceased on 28 February.

Legal documents published in South Africa detail for the first time an elaborate system of alleged money-laundering set up under Evans in the 1990s. According to statements obtained from offshore lawyers, senior BAE executives proposed in 1996 that a Liechtenstein bank should register a covert offshore company with the intention of concealing all links with BAE.

The three BAE directors of the secret entity, Red Diamond, were named in the statements as Hugh Dickinson, Philip Riley and Jeremy Wooding.

The statements allege a meeting took place in Zurich to set up disguised conduits which sent more than £100m to agents in South Africa. BAE wanted to cement a huge $2bn deal to sell planes which were twice the price of an Italian rival. The South African cabinet agreed the deal in 1998-9.

Cash to middlemen is said to have flowed through a long series of front companies and offshore jurisdictions. Red Diamond paid money into a Liechtenstein bank account controlled by a BVI-registered entity called Arstow. Arstow itself is said to have passed millions of pounds to yet another offshore company, Westunity. Cash is then said to have moved on to another company with an account in Hong Kong that belonged to Fana Hlongwane, an adviser to the South African minister of defence, Joe Modise.

The documents came to light as a result of the original SFO investigation, and were used by South African authorities in an initially successful freezing of Hlongwane's accounts. The South African prosecutor then dropped the proceedings.

The SFO has failed to press home a criminal case against BAE over the South African deals, in part because of the lack of enthusiasm of the ANC regime.